The nuclear power plant has been required to reduce the cost for the purpose of making the low-cost energy since several years ago in Japan. The Heating, Ventilating and Air Conditioning system in the nuclear power plant has been also required to reduce its cost. On the other hand the ventilation system should add the improvable function according to the advanced plant design. In response to these different requirements, the ventilation criteria and the design of the ventilation system have been evaluated and optimized in Japanese PWR Plant design.

This paper presents the findings of our study as follows:

• A successful example of a combined system is presented in which the number of fans and units decreased, and suitable conditions for combining systems are discussed.
• A new criterion of ventilation flow rate is developed, which is considered the appropriate flow rate to reduce the concentration of airborne radioactive particles to the allowable level by using the concept of DAC (derived air concentration) based on recommendations of the International Commission on Radiological Protection (ICRP), Publication 30.
• The criterion of using the maintenance exhaust to remove airborne radioactive particles from the maintenance working area is developed, which is based on the practice of the maintenance work in Japanese PWR plants.
• The application of the chilled-water cooling unit for an auxiliary building ventilation system has been evaluated from the viewpoint of cost reduction. Its possibilities and the conditions to which it applies in a Japanese PWR plant are discussed.

As a result of these measures, the ventilation system is simplified and the capacity of the control area’s ventilation system is decreased about 20% compared with current design. The maintenance exhaust provision is provided to reduce the inhalant exposure.

Units: SI